Submitted to: Decennial National Irrigation Symposium
Publication Type: Proceedings
Publication Acceptance Date: November 14, 2000
Publication Date: N/A
Interpretive Summary: Irrigation is the principal method for increasing crop yields in regions with precipitation that is inadequate or too erratic to meet the crop needs. Irrigation requires large quantities of high quality water. The purpose of this paper was to review irrigation from a world level, from the United States' level, and to discuss methods for improving the crop yield per unit of water used in irrigated agriculture. In the world, about 650 million acres (about 15% of the cultivated land) produces about 36% of the world's food. In the U.S., irrigated lands have increased by 5.65 million acres from 1992 to 1997 and total about 50 million acres. In the U.S., significant changes have occurred in the irrigation technology with a shift to center pivots and drip and a decline in surface irrigation. Water use efficiency (WUE) is defined as the crop yield per unit of water use. Agronomy and engineering are the predominate means for enhancing WUE. But WUE can be increased by reducing losses of water to unusable water sources with degraded quality and by reallocating water to its highest use. The last item is strongly linked to societal aspects affecting water use and regulations.
Technical Abstract: Irrigated agriculture is a vital component of total agriculture and supplies many of the fruits, vegetables, and cereal foods consumed by humans; the grains fed to animals that are used as human food; and the feed to sustain animals for work in many parts of the world. World-wide irrigation was practiced on about 263 million ha in 1996 with about 49% of the world's irrigation in India, China, and the United States. The objectives of this paper are to review irrigation worldwide in meeting our growing needs for food production, irrigation trends in the U.S., to discuss various concepts that define water use efficiency (WUE) in irrigated agriculture from both an engineering and agronomic view points, and to discuss the impacts of enhanced WUE on water conservation. Frequent reports indicate that scarcely one-third of our rainfall, surface water, or groundwater is used to produce plants useful to mankind. Without appropriate management, irrigated agriculture can be detrimental to the environment and can endanger sustainability. Irrigated agriculture is facing growing competition for low-cost, high-quality water. WUE in irrigated agriculture is broader in scope than most agronomic applications and must be considered on a watershed, basin, irrigation district, or catchment scale. The main pathways for enhancing WUE in irrigated agriculture are to increase the output per unit of water (engineering and agronomic management aspects), reduce losses of water to unusable sinks and reduce water degradation (environmental aspects), and reallocating water to higher priority uses (societal aspects).